This invention relates generally to the fields of polymer chemistry, lithography, and semiconductor fabrication. More specifically, the invention relates to novel aromatic polymers, particularly fluorine-containing styrene acrylate copolymers, which are useful in lithographic photoresist compositions, particularly chemical amplification photoresist compositions including ultraviolet, electron-beam, and x-ray photoresists.
There is a desire in the industry for higher circuit density in microelectronic devices made using lithographic techniques. One method of increasing the number of components per chip is to decrease the minimum feature size on the chip, which requires higher lithographic resolution. This has been accomplished over the past twenty years by reducing the wavelength of the imaging radiation from the visible (436 nm) down through the ultraviolet (365 nm) to the deep ultraviolet (DUV) at 248 nm. Development of commercial lithographic processes using ultra-deep ultraviolet radiation, particularly 193 nm, is now becoming of interest. See, for example, Allen et al. (1995), xe2x80x9cResolution and Etch Resistance of a Family of 193 nm Positive Resists,xe2x80x9d J. Photopolym. Sci. and Tech. 8(4):623-636, and Abe et al. (1995), xe2x80x9cStudy of ArF Resist Material in Terms of Transparency and Dry Etch Resistance,xe2x80x9d J. Photopolym. Sci. and Tech. 8(4):637-642. The resists proposed for use with 193 nm imaging radiation do not appear suitable for use with 157 nm radiation due to their poor transparency at the 157 nm wavelength.
Certain attempts have been made to develop 157 nm resists, for example using heavily fluorinated materials such as polytetrafluoroethylene (e.g., Teflon AF(copyright); see Endert et al. (1999) Proc. SPIE-Int. Soc. Opt. Eng, 3618:413-417) or hydridosilsesquioxanes (see U.S. Pat. No. 6,087,064 to Lin et al.). These materials do not, however, have the requisite reactivity or solubility characteristics. The challenge in developing chemically amplified resists for 157 nm lithography is in achieving suitable transparency in polymers that have acid-labile functionalities and developed with industry standard developers in either exposed or unexposed areas depending on whether the resist is positive or negative.
Polymers prepared from trifluoromethyl-substituted acrylates have been described. See, for example, Ito et al. (1981), xe2x80x9cMethyl Alpha-Trifluoromethylacrylate, an E-Beam and UV Resist,xe2x80x9d IBM Technical Disclosure Bulletin 24(4):991, Ito et al. (1982) Macromolecules 15:915-920, which describes preparation of poly(methyl xcex1-trifluoromethylacrylate) and poly(xcex1-trifluoromethylacrylonitrile) from their respective monomers, and Ito et al. (1987), xe2x80x9cAnionic Polymerization of xcex1-(Trifluoromethyl)Acrylate,xe2x80x9d in Recent Advances in Anionic Polymerization, T. E. Hogen-Esch and J. Smid, Eds. (Elsevier Science Publishing Co., Inc.), which describes an anionic polymerization method for preparing polymers of trifluoromethylacrylate. Willson et al., Polymer Engineering and Science 23(18):1000-1003, also discuss poly(methyl xcex1-trifluoromethylacrylate) and use thereof in a positive electron beam resist. However, none of these references discloses the utility of trifluoromethyl-substituted acrylate polymers in chemical amplification resists.
Polymers derived from poly(4-hydroxystyrene), or xe2x80x9cPHOSTxe2x80x9d, have been favored for work at 248 nm, since the phenolic structure provides dry etch stability, aqueous base solubility, and optical transparency at 248 nm. (See xe2x80x9cDeep UV resists: evolution and statusxe2x80x9d, H. Ito, Solid State Technol., 36(7), pp. 164-173, 1996.) One important example is the xe2x80x9cESCAPxe2x80x9d resist, which is formed from a copolymer of hydroxystyrene (xe2x80x9cHOSTxe2x80x9d) and t-butyl acrylate (TBA). (See xe2x80x9cEnvironmentally stable chemical amplification positive resist: principle, chemistry, contamination resistance, and lithographic feasibilityxe2x80x9d, H. Ito et al., J. Photopolym. Sci. Technol., 7, pp. 433-448, 1994; and xe2x80x9cThe lithographic performance of an environmentally stable chemically amplified photoresist (ESCAP)xe2x80x9d, W. Conley et al., Proc. SPIE, 2724, pp. 34-60, 1996.) The ESCAP resist, or poly(HOST-co-TBA), has become foundational to 248 nm photolithography. Poly(4-(1-hydroxy-2,2,2-trifluoro-1-trifluoromethyl)ethylstyrene), or PSHFI, has been suggested as a replacement for PHOST for 248 nm lithography (see xe2x80x9cHexafluoroacetone in resist chemistry: a versatile new concept for materials for deep UV lithographyxe2x80x9d, K. J. Przybilla et al., Proc. SPIE, 1672, pp. 500-512, 1992), but commercial resist products have not yet emerged.
Styrenic polymers have not been favored for work at 193 nm because of the absorption arising from the aromatic group. For the same reason, it has been commonly believed that aromatic polymers would not find photolithography applications at 157 nm: The optical densities of PHOST and ESCAP at this wavelength are 6.5/micron and 7/micron, respectively. Accordingly, the search for resists for use at 157 nm has focused on other polymers such as aliphatic polymers, which present challenging problems of their own, e.g., poor etch resistance.
Accordingly, it is a primary object of the invention to address the above-described need in the art by providing novel fluorine-containing styrene acrylate copolymers suitable for use in lithographic photoresist compositions.
It is another object of the invention to provide a lithographic photoresist composition containing a fluorine-containing styrene acrylate copolymer.
It is still another object of the invention to provide such a composition wherein the fluorine-containing styrene acrylate copolymer is relatively transparent in certain wavelength regions in the deep ultraviolet spectrum (i.e., below 250 nm), and in particular, at 248 nm and 157 nm.
It is yet another object of the invention to provide such a composition wherein the fluorine-containing styrene acrylate copolymer is a copolymer of a styrene monomer substituted with a fluorine-containing moiety and a fluorinated or non-fluorinated acrylic monomer.
It is still another object of the invention to provide a method for generating a resist image on a substrate using a photoresist composition as described herein.
It is a further object of the invention to provide a method for forming a patterned material structure on a substrate by transferring the aforementioned resist image to the material through, for example, etching.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.
In one aspect, then, the present invention relates to a fluorine-containing styrene acrylate copolymer prepared by copolymerization of at least one aromatic monomer having the structure of formula (I) 
and at least one monomer having the structure of formula (II) 
wherein:
m is zero or 1;
n is an integer in the range of zero to 4 inclusive;
R1 is H, F, lower alkyl, or fluorinated lower alkyl;
R2 is alkyl, fluorinated alkyl, hydroxyl, alkoxy, fluorinated alkoxy, halogen, or cyano;
R3 is a fluorinated alkyl;
R4 is H, alkyl, or fluorinated alkyl; where R8 is H or alkyl, R9 is alkyl, and R10 is alkyl or alkoxy;
R6 is H, F, lower alkyl, or fluorinated lower alkyl;
R7 is selected from the group consisting of H, an acid-labile moiety optionally substituted with one or more fluorine atoms, and an acid inert moiety optionally substituted with one or more fluorine atoms;
L is a hydrocarbylene linking group optionally substituted with one or more fluorine atoms; and
Ar is an aromatic moiety.
In another aspect, the invention relates to a lithographic photoresist composition comprising a fluorine-containing styrene acrylate copolymer as described above and a photosensitive acid generator (also referred to herein as a xe2x80x9cphotoacid generator,xe2x80x9d a xe2x80x9cPAG,xe2x80x9d or a xe2x80x9cradiation-sensitive acid generatorxe2x80x9d).
One aspect of the invention also relates to the use of the resist composition in a lithography method. The process involves the steps of (a) coating a substrate (e.g., a ceramic, metal or semiconductor substrate) with a film comprising a radiation-sensitive acid generator and a copolymer as provided herein; (b) exposing the film selectively to a predetermined pattern of radiation to form a latent image therein; and (c) developing the image using a suitable developer composition. The radiation may be ultraviolet, electron beam or x-ray. Ultraviolet radiation is preferred, particularly deep ultraviolet radiation at 157 nm or 248 nm, or even extreme ultraviolet radiation at, for example, 13 nm. The pattern from the resist structure may then be transferred to the underlying substrate. Typically, the transfer is achieved by reactive ion etching or some other etching technique. Thus, the compositions provided herein and the resulting resist structures can be used to create patterned material layer structures such as metal wiring lines, holes for contacts or vias, insulation sections (e.g., damascene trenches or shallow trench isolation), trenches for capacitor structures, etc. as might be used in the design of integrated circuit devices.
Another aspect of the invention is a method of forming a patterned material structure on a substrate, in which the material is selected from the group consisting of semiconductors, ceramics and metals. The method includes providing a substrate having a surface comprised of the material. A resist composition is applied to the substrate surface to form a resist layer over the material, in which the resist composition comprises a copolymer as provided herein and a radiation-sensitive acid generator. The resist is patternwise exposed to radiation, whereby acid is generated by the radiation-sensitive acid generator in exposed regions of the resist layer. The resist is contacted with a developer solution, whereby the developed regions of the resist layer reveal a patterned resist structure, and the resist structure pattern is transferred to the material by etching into the material through spaces in the resist structure.